In recent years, insulated gate bipolar transistors (IGBTs), diodes, and the like are used as semiconductor devices used in power conversion devices such as inverters. The diodes are generally connected in an antiparallel manner to the IGBTs and are used as refluxing diodes. Because of this, the diodes are sometimes referred to as free wheeling diodes (FWDs).
Characteristic improvement of the FWDs is crucial on a par with characteristic improvement of the IGBTs in characteristic improvement of the power conversion devices such as the inverters. Crucial characteristics of the FWDs include an ON voltage (a voltage drop in a conduction state), a recovery time (an extinction time of a recovery current upon reverse recovery), a safe operation region upon recovery (a region not destroyed even if a voltage is applied in a state where the recovery current is flowing), and the like. Moreover, a smaller current and voltage oscillation upon recovery is more desirable. Among these, widening the safe operation region upon recovery while shortening the recovery time is crucial.